1. Technical Field
The present invention relates to a zoom lens system, a lens barrel, an imaging device and a camera. In particular, the present invention relates to: a zoom lens system that is used suitably in a small and high-image quality camera such as a digital still camera or a digital video camera, and that has a large variable magnification ratio and a high resolution; a lens barrel that holds this zoom lens system and has a short overall length at the time of accommodation as well as a low overall height; an imaging device including this lens barrel; and a thin and compact camera employing this imaging device.
2. Description of the Background Art
With recent progress in the development of solid-state image sensors such as a CCD (Charge Coupled Device) and a CMOS (Complementary Metal-Oxide Semiconductor) having a high pixel, digital still cameras and digital video cameras are rapidly spreading that employ an imaging device including an imaging optical system of high optical performance corresponding to the above solid-state image sensors of a high pixel.
Among these, especially in digital still cameras, thin constructions have recently been proposed in order to achieve satisfactory accommodation property or portability to which the highest priority is imparted. As possible means for realizing such thin digital still cameras, a large number of zoom lens systems have been proposed that bend a light beam by 90°.
For example, Japanese Laid-Open Patent Publication No. 2004-004533 and No. 2003-202500 disclose a construction in which in an imaging device provided with a zoom lens system, a right-angle prism provided with an internal reflecting surface for bending a light beam by 90° is arranged inside a lens unit located on the most object side. In the imaging device disclosed in Japanese Laid-Open Patent Publication No. 2004-004533 and No. 2003-202500, since the object light is bent in a plane perpendicular to the optical axis of the incident lens unit, the thickness of the imaging device is determined by the right-angle prism and the lens elements located on the object side relative to the right-angle prism. This reduces the thickness.
Further, Japanese Laid-Open Patent Publication No. 2004-102089 discloses a construction in which in an imaging device provided with a zoom lens system composed of four units having a construction of positive, negative, positive and positive, a right-angle prism provided with an internal reflecting surface for bending a light beam by 90° is arranged inside a second lens unit having negative optical power. In the imaging device described in Japanese Laid-Open Patent Publication No. 2004-102089, the right-angle prism can be arranged inside the lens unit located on the image side relative to the first lens unit having positive optical power. This allows the right-angle prism to be constructed compactly.
Nevertheless, in the zoom lens system disclosed in Japanese Laid-Open Patent Publication No. 2004-004533, although a compact imaging device can be provided, the variable magnification ratio is as small as approximately 3. Further, the optical performance is insufficient in the periphery.
Further, in the zoom lens system disclosed in Japanese Laid-Open Patent Publication No. 2003-202500 and No. 2004-102089, thickness reduction of the imaging device is restricted from their intrinsic construction. Further, optical performance is insufficient in the periphery part.